真 C 語言實做 Functional Language 的 Currying

by thinker

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jserv 寫了一篇 linkname:[$C$ 語言實做 Functional Language 的 Currying] http://blog.linux.org.tw/~jserv/archives/002029.html ，結果根本不是用 $C$ 實作，其中使用了大量的 assembly 或者是 opcode，讓我大呼「中招了」。既然如此，我就重新 implement 一個完全使用 $C$ 的 「真 $C$ 語言」 版本。本$範例$基本上分成兩個部分，前半部著眼於「收集參數，最後才將參數傳送給 target function ，並執行」，後半部著眼於「如何將資料和 target function 包裝成一個 partial function 的外觀」。

{{{#!cpp
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ERROR()

typedef struct _curry {
  void *func;
  int max;
  int cur_sz;
  char *buf;
} curry_t;

void _new_curry(curry_t *co, void *func) {
  co->func = func;
  co->max = 32;
  co->cur_sz = 0;
  co->buf = (char *)malloc(32);
}

curry_t *new_curry(void *func) {
  curry_t *co;
  
  co = (curry_t *)malloc(sizeof(curry_t));
  _new_curry(co, func);
  return co;
}

void partial(curry_t *co, int dsz, void *d) {
  int new_sz;
  char *new_buf;
  
  new_sz = co->cur_sz + dsz;
  if(new_sz > co->max) {
    new_buf = realloc(co->buf, ((new_sz + 31) / 32) * 32);
    if(new_buf == NULL) {
      ERROR();
    }
    co->buf = new_buf;
  }
  memcpy(co->buf + co->cur_sz, d, dsz);
  co->cur_sz = new_sz;
}
void *_partial = &partial;

#define PARTIAL(co, d) ((void (*)(void *, int, ...))_partial)(co, sizeof(d), d)

char *dummy(int a) {
  return (char *)&a;
}

int complete(curry_t *co) {
  char *buf;
  int r;
  
  alloca(co->cur_sz);
  buf = dummy(0);
  memcpy(buf, co->buf, co->cur_sz);
  if(co->cur_sz > 0) {
    r = (*(int (*)(int))co->func)(*(int *)buf);
  } else {
    r = (*(int (*)())co->func)();
  }
  
  return r;
}

int foo(int a, int b) {
  return a + b;
}

/* ------------------------------------------------------------- */
typedef int (*intf)(int);

int obj_diff = 0;

int set_diff(void *a) {
  obj_diff = (int)*(char **)((char *)(&a) - sizeof(void *));
  return 0;
}

int add_part(void *a) {
  char *buf;
  curry_t *co;
  
  buf = *(char **)((char *)&a - sizeof(void *)) + obj_diff;
  co = (curry_t *)buf;
  partial(co, sizeof(int), a);
  return 0;
}

int (*partial_worker)(void *) = (int(*)(void *))&set_diff;

void *partial_call(int a) {
  return (void*)partial_worker(&a);
}

int partial_sz;

void partial_init(void) {
  void *buf;
  
  partial_sz = ((char *)partial_init - (char *)partial_call + 3) & ~0x3;
  
  buf = malloc(partial_sz + sizeof(curry_t));
  memcpy(buf, partial_call, partial_sz);
  ((void (*)(void))buf)();
  
  obj_diff = (int)buf + partial_sz - obj_diff;
  partial_worker = add_part;
  free(buf);
}

intf new_partial(void *func) {
  char *buf;
  
  buf = malloc(partial_sz + sizeof(curry_t));
  _new_curry((curry_t *)(buf + partial_sz), func);
  memcpy(buf, partial_call, partial_sz);
  
  return (intf)buf;
}

int partial_result(intf f) {
  curry_t *co;
  
  co = (curry_t *)((char *)f + partial_sz);
  return complete(co);
}

int
main(int argc, const char *argv[]) {
  
  int r, a;
  curry_t *co;
  intf f;
  
  co = new_curry(foo);
  a = 3;
  PARTIAL(co, &a);
  a = 9;
  PARTIAL(co, &a);
  r = complete(co);
  printf("%d\n", r);
  
  partial_init();
  f = new_partial(foo);
  f(33);
  f(21);
  printf("%d\n", partial_result(f));
  
  return 0;
}
}}}

看不懂嗎? 所有的解釋都在 linkname:[這裡] http://blog.linux.org.tw/~jserv/archives/002029.html 。抱歉，我是個懶人，還好有 $hyperlink$ 這個東西。

本程只是一個測試，有些 memory 沒釋放，請勿直接 production 使用 :p

== 相關 ==
* linkname:[真 $C$ 之二] http://heaven.branda.to/~thinker/GinGin_CGI.py/show_id_doc/327
* linkname:[真 $C$ 之三] http://heaven.branda.to/~thinker/GinGin_CGI.py/show_id_doc/328

最後更新時間: 2008-06-19 16:42:43 CST | 引用

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